Definition of polemoscope in US English:

polemoscope

noun

historical
  • An optical instrument fitted with a mirror or pair of mirrors set at an angle to the line of sight, for use in viewing objects not directly before the eye.

Origin

Mid 17th century; earliest use found in John Beale (bap. 1608, d. 1683), Church of England clergyman and writer on agriculture and natural philosophy. From post-classical Latin polemoscopium (J. Hevelius Selenographia Prolegomena 24) from ancient Greek πολεμο- + post-classical Latin -scopium.